Check If N and Its Double Exist

Check If N and Its Double Exist

Given an array arr of integers, check if there exists two integers N and M such that N is the double of M ( i.e. N = 2 * M).

More formally check if there exists two indices i and j such that :

• i != j

• 0 <= i, j < arr.length

• arr[i] == 2 * arr[j]

Example 1:

Input: arr = [10,2,5,3]
Output: true
Explanation: N = 10 is the double of M = 5,that is, 10 = 2 * 5.

Example 2:

Input: arr = [7,1,14,11]
Output: true
Explanation: N = 14 is the double of M = 7,that is, 14 = 2 * 7.

Example 3:

Input: arr = [3,1,7,11]
Output: false
Explanation: In this case does not exist N and M, such that N = 2 * M.

Constraints:

• 2 <= arr.length <= 500

• -10^3 <= arr[i] <= 10^3

Solutions

🧠 Cpp

#define all(x) (x).begin(), (x).end()

class Solution
{
public:
    bool checkIfExist(vector<int>& arr)
    {
        //O(n^2) solution
        for(auto iter = begin(arr); iter < end(arr); ++iter)
        {
            auto found = find(all(arr), *iter*2);
            if( found != arr.end() && found != iter)
                return true;
        }

        return false;
    }
};